What is the best way to reduce the poly count on this object with smooth shading
I see that you are using Blender 2.8 so you can make this object super low poly with new features in Bevel modifier.

Object:

You can create object in two ways. Quad based (edge loops) or simple Boolean.



Modifier:

Add Bevel modifier, check Harden Normals, switch mode to Angle and optionally change Outer Miter to Arc.



To be able to see the result, you will need to turn on Autosmooth and of course Shading Smooth.